FlexRadio wiring circuit for Bose QC-25 Headset with MIC Boom (Electret MIC)

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The FlexRadio 6400 uses a ‘pseudo-balanced’ MIC input but the manual is not very helpful when it describes this as “ mic (+) and mic (-) lines are balanced all the way to the input of the A/D converter, where the mic (-) line is DC grounded.”

Fortunately I was able find this circuit from Dale K4DC on the flexradio community support forum originally designed for the Yamaha CM-500.  This design works with my Bose QC-25 headset (2014) and my Koss SB 45 (2021).  

I made two adapters, first one without the 10pF capacitor because I didn’t have one on hand.  I did not notice any impact on transmit audio quality.  I added the capacitor a few days later for permanent use.  I get great audio reports. 




Reminder that the electret MIC requires you to enable BIAS voltage in SmartSDR radio set up.  For the BOSE headset I’m using this mic boom adapter (2021):

Reference thread on the FlexRadio Community Support Forum:

https://community.flexradio.com/discussion/7700793/wiring-a-yamaha-cm500-headset-for-a-6400-m-or-6600-m

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